Add cascade setting to enable/disable AI false positive detection

What does this MR do and why?

This MR introduces backend for setting to enable/disable AI false positive detection

How to set up and validate locally

1. Enable feature flag ai_experiment_sast_fp_detection
2. Run migrations in this MR
3. Observe duo_sast_fp_detection_enabled, duo_sast_fp_detection_availability, duo_sast_fp_detection_enabled_locked? methods on

• ApplicationSetting
• NamespaceSetting
• ProjectSetting

4. Make sure it follows cascade behavior - setting enabled to false will disable same value in cascade in groups

MR acceptance checklist

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Related to #577216 (closed)